<!DOCTYPE HTML>
<html lang="zh-CN">


<head>
    <meta charset="utf-8">
    <meta name="keywords" content="Spring Boot 入门, Gtwff">
    <meta name="description" content="">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0, user-scalable=no">
    <meta name="renderer" content="webkit|ie-stand|ie-comp">
    <meta name="mobile-web-app-capable" content="yes">
    <meta name="format-detection" content="telephone=no">
    <meta name="apple-mobile-web-app-capable" content="yes">
    <meta name="apple-mobile-web-app-status-bar-style" content="black-translucent">
    <meta name="referrer" content="no-referrer-when-downgrade">
    <!-- Global site tag (gtag.js) - Google Analytics -->

<script async src="https://www.googletagmanager.com/gtag/js?id="></script>
<script>
    window.dataLayer = window.dataLayer || [];
    function gtag() {
        dataLayer.push(arguments);
    }

    gtag('js', new Date());
    gtag('config', '');
</script>


    <title>Spring Boot 入门 | Gtwff</title>
    <link rel="icon" type="image/png" href="/favicon.png">

    <link rel="stylesheet" type="text/css" href="/libs/awesome/css/all.css">
    <link rel="stylesheet" type="text/css" href="/libs/materialize/materialize.min.css">
    <link rel="stylesheet" type="text/css" href="/libs/aos/aos.css">
    <link rel="stylesheet" type="text/css" href="/libs/animate/animate.min.css">
    <link rel="stylesheet" type="text/css" href="/libs/lightGallery/css/lightgallery.min.css">
    <link rel="stylesheet" type="text/css" href="/css/matery.css">
    <link rel="stylesheet" type="text/css" href="/css/my.css">

    <script src="/libs/jquery/jquery.min.js"></script>

<meta name="generator" content="Hexo 5.4.0"></head>



   <style>
    body{
       background-image: url(https://cdn.jsdelivr.net/gh/Tokisaki-Galaxy/res/site/medias/background.jpg);
       background-repeat:no-repeat;
       background-size:cover;
       background-attachment:fixed;
    }
</style>



<body>
    <header class="navbar-fixed">
    <nav id="headNav" class="bg-color nav-transparent">
        <div id="navContainer" class="nav-wrapper container">
            <div class="brand-logo">
                <a href="/" class="waves-effect waves-light">
                    
                    <img src="/medias/logo.png" class="logo-img" alt="LOGO">
                    
                    <span class="logo-span">Gtwff</span>
                </a>
            </div>
            

<a href="#" data-target="mobile-nav" class="sidenav-trigger button-collapse"><i class="fas fa-bars"></i></a>
<ul class="right nav-menu">
  
  <li class="hide-on-med-and-down nav-item">
    
    <a href="/" class="waves-effect waves-light">
      
      <i class="fas fa-home" style="zoom: 0.6;"></i>
      
      <span>首页</span>
    </a>
    
  </li>
  
  <li class="hide-on-med-and-down nav-item">
    
    <a href="/tags" class="waves-effect waves-light">
      
      <i class="fas fa-tags" style="zoom: 0.6;"></i>
      
      <span>标签</span>
    </a>
    
  </li>
  
  <li class="hide-on-med-and-down nav-item">
    
    <a href="/categories" class="waves-effect waves-light">
      
      <i class="fas fa-bookmark" style="zoom: 0.6;"></i>
      
      <span>分类</span>
    </a>
    
  </li>
  
  <li class="hide-on-med-and-down nav-item">
    
    <a href="/archives" class="waves-effect waves-light">
      
      <i class="fas fa-archive" style="zoom: 0.6;"></i>
      
      <span>归档</span>
    </a>
    
  </li>
  
  <li class="hide-on-med-and-down nav-item">
    
    <a href="/about" class="waves-effect waves-light">
      
      <i class="fas fa-user-circle" style="zoom: 0.6;"></i>
      
      <span>关于</span>
    </a>
    
  </li>
  
  <li class="hide-on-med-and-down nav-item">
    
    <a href="/contact" class="waves-effect waves-light">
      
      <i class="fas fa-comments" style="zoom: 0.6;"></i>
      
      <span>留言板</span>
    </a>
    
  </li>
  
  <li class="hide-on-med-and-down nav-item">
    
    <a href="/friends" class="waves-effect waves-light">
      
      <i class="fas fa-address-book" style="zoom: 0.6;"></i>
      
      <span>友情链接</span>
    </a>
    
  </li>
  
  <li>
    <a href="#searchModal" class="modal-trigger waves-effect waves-light">
      <i id="searchIcon" class="fas fa-search" title="搜索" style="zoom: 0.85;"></i>
    </a>
  </li>
</ul>


<div id="mobile-nav" class="side-nav sidenav">

    <div class="mobile-head bg-color">
        
        <img src="/medias/logo.png" class="logo-img circle responsive-img">
        
        <div class="logo-name">Gtwff</div>
        <div class="logo-desc">
            
            Never really desperate, only the lost of the soul.
            
        </div>
    </div>

    <ul class="menu-list mobile-menu-list">
        
        <li class="m-nav-item">
	  
		<a href="/" class="waves-effect waves-light">
			
			    <i class="fa-fw fas fa-home"></i>
			
			首页
		</a>
          
        </li>
        
        <li class="m-nav-item">
	  
		<a href="/tags" class="waves-effect waves-light">
			
			    <i class="fa-fw fas fa-tags"></i>
			
			标签
		</a>
          
        </li>
        
        <li class="m-nav-item">
	  
		<a href="/categories" class="waves-effect waves-light">
			
			    <i class="fa-fw fas fa-bookmark"></i>
			
			分类
		</a>
          
        </li>
        
        <li class="m-nav-item">
	  
		<a href="/archives" class="waves-effect waves-light">
			
			    <i class="fa-fw fas fa-archive"></i>
			
			归档
		</a>
          
        </li>
        
        <li class="m-nav-item">
	  
		<a href="/about" class="waves-effect waves-light">
			
			    <i class="fa-fw fas fa-user-circle"></i>
			
			关于
		</a>
          
        </li>
        
        <li class="m-nav-item">
	  
		<a href="/contact" class="waves-effect waves-light">
			
			    <i class="fa-fw fas fa-comments"></i>
			
			留言板
		</a>
          
        </li>
        
        <li class="m-nav-item">
	  
		<a href="/friends" class="waves-effect waves-light">
			
			    <i class="fa-fw fas fa-address-book"></i>
			
			友情链接
		</a>
          
        </li>
        
        
        <li><div class="divider"></div></li>
        <li>
            <a href="https://gitee.com/kuangty/kuangty" class="waves-effect waves-light" target="_blank">
                <i class="fab fa-github-square fa-fw"></i>Fork Me
            </a>
        </li>
        
    </ul>
</div>


        </div>

        
            <style>
    .nav-transparent .github-corner {
        display: none !important;
    }

    .github-corner {
        position: absolute;
        z-index: 10;
        top: 0;
        right: 0;
        border: 0;
        transform: scale(1.1);
    }

    .github-corner svg {
        color: #0f9d58;
        fill: #fff;
        height: 64px;
        width: 64px;
    }

    .github-corner:hover .octo-arm {
        animation: a 0.56s ease-in-out;
    }

    .github-corner .octo-arm {
        animation: none;
    }

    @keyframes a {
        0%,
        to {
            transform: rotate(0);
        }
        20%,
        60% {
            transform: rotate(-25deg);
        }
        40%,
        80% {
            transform: rotate(10deg);
        }
    }
</style>

<a href="https://gitee.com/kuangty/kuangty" class="github-corner tooltipped hide-on-med-and-down" target="_blank"
   data-tooltip="Fork Me" data-position="left" data-delay="50">
    <svg viewBox="0 0 250 250" aria-hidden="true">
        <path d="M0,0 L115,115 L130,115 L142,142 L250,250 L250,0 Z"></path>
        <path d="M128.3,109.0 C113.8,99.7 119.0,89.6 119.0,89.6 C122.0,82.7 120.5,78.6 120.5,78.6 C119.2,72.0 123.4,76.3 123.4,76.3 C127.3,80.9 125.5,87.3 125.5,87.3 C122.9,97.6 130.6,101.9 134.4,103.2"
              fill="currentColor" style="transform-origin: 130px 106px;" class="octo-arm"></path>
        <path d="M115.0,115.0 C114.9,115.1 118.7,116.5 119.8,115.4 L133.7,101.6 C136.9,99.2 139.9,98.4 142.2,98.6 C133.8,88.0 127.5,74.4 143.8,58.0 C148.5,53.4 154.0,51.2 159.7,51.0 C160.3,49.4 163.2,43.6 171.4,40.1 C171.4,40.1 176.1,42.5 178.8,56.2 C183.1,58.6 187.2,61.8 190.9,65.4 C194.5,69.0 197.7,73.2 200.1,77.6 C213.8,80.2 216.3,84.9 216.3,84.9 C212.7,93.1 206.9,96.0 205.4,96.6 C205.1,102.4 203.0,107.8 198.3,112.5 C181.9,128.9 168.3,122.5 157.7,114.1 C157.9,116.9 156.7,120.9 152.7,124.9 L141.0,136.5 C139.8,137.7 141.6,141.9 141.8,141.8 Z"
              fill="currentColor" class="octo-body"></path>
    </svg>
</a>
        
    </nav>

</header>

    



<div class="bg-cover pd-header post-cover" style="background-image: url('/medias/featureimages/6.jpg')">
    <div class="container" style="right: 0px;left: 0px;">
        <div class="row">
            <div class="col s12 m12 l12">
                <div class="brand">
                    <h1 class="description center-align post-title">Spring Boot 入门</h1>
                </div>
            </div>
        </div>
    </div>
</div>




<main class="post-container content">

    
    <link rel="stylesheet" href="/libs/tocbot/tocbot.css">
<style>
    #articleContent h1::before,
    #articleContent h2::before,
    #articleContent h3::before,
    #articleContent h4::before,
    #articleContent h5::before,
    #articleContent h6::before {
        display: block;
        content: " ";
        height: 100px;
        margin-top: -100px;
        visibility: hidden;
    }

    #articleContent :focus {
        outline: none;
    }

    .toc-fixed {
        position: fixed;
        top: 64px;
    }

    .toc-widget {
        width: 345px;
        padding-left: 20px;
    }

    .toc-widget .toc-title {
        padding: 35px 0 15px 17px;
        font-size: 1.5rem;
        font-weight: bold;
        line-height: 1.5rem;
    }

    .toc-widget ol {
        padding: 0;
        list-style: none;
    }

    #toc-content {
        padding-bottom: 30px;
        overflow: auto;
    }

    #toc-content ol {
        padding-left: 10px;
    }

    #toc-content ol li {
        padding-left: 10px;
    }

    #toc-content .toc-link:hover {
        color: #42b983;
        font-weight: 700;
        text-decoration: underline;
    }

    #toc-content .toc-link::before {
        background-color: transparent;
        max-height: 25px;

        position: absolute;
        right: 23.5vw;
        display: block;
    }

    #toc-content .is-active-link {
        color: #42b983;
    }

    #floating-toc-btn {
        position: fixed;
        right: 15px;
        bottom: 76px;
        padding-top: 15px;
        margin-bottom: 0;
        z-index: 998;
    }

    #floating-toc-btn .btn-floating {
        width: 48px;
        height: 48px;
    }

    #floating-toc-btn .btn-floating i {
        line-height: 48px;
        font-size: 1.4rem;
    }
</style>
<div class="row">
    <div id="main-content" class="col s12 m12 l9">
        <!-- 文章内容详情 -->
<div id="artDetail">
    <div class="card">
        <div class="card-content article-info">
            <div class="row tag-cate">
                <div class="col s7">
                    
                    <div class="article-tag">
                        
                            <a href="/tags/Spring-Boot-%E5%85%A5%E9%97%A8/">
                                <span class="chip bg-color">Spring Boot 入门</span>
                            </a>
                        
                    </div>
                    
                </div>
                <div class="col s5 right-align">
                    
                    <div class="post-cate">
                        <i class="fas fa-bookmark fa-fw icon-category"></i>
                        
                            <a href="/categories/Spring-Boot/" class="post-category">
                                Spring Boot
                            </a>
                        
                    </div>
                    
                </div>
            </div>

            <div class="post-info">
                
                <div class="post-date info-break-policy">
                    <i class="far fa-calendar-minus fa-fw"></i>发布日期:&nbsp;&nbsp;
                    2022-02-19
                </div>
                

                
                <div class="post-date info-break-policy">
                    <i class="far fa-calendar-check fa-fw"></i>更新日期:&nbsp;&nbsp;
                    2022-02-19
                </div>
                

                
                <div class="info-break-policy">
                    <i class="far fa-file-word fa-fw"></i>文章字数:&nbsp;&nbsp;
                    3.7k
                </div>
                

                
                <div class="info-break-policy">
                    <i class="far fa-clock fa-fw"></i>阅读时长:&nbsp;&nbsp;
                    15 分
                </div>
                

                
                    <div id="busuanzi_container_page_pv" class="info-break-policy">
                        <i class="far fa-eye fa-fw"></i>阅读次数:&nbsp;&nbsp;
                        <span id="busuanzi_value_page_pv"></span>
                    </div>
				
            </div>
        </div>
        <hr class="clearfix">

        
        <!-- 是否加载使用自带的 prismjs. -->
        <link rel="stylesheet" href="/libs/prism/prism.css">
        

        
        <!-- 代码块折行 -->
        <style type="text/css">
            code[class*="language-"], pre[class*="language-"] { white-space: pre-wrap !important; }
        </style>
        

        <div class="card-content article-card-content">
            <div id="articleContent">
                <h1 id="🚪-Spring-Boot-入门"><a href="#🚪-Spring-Boot-入门" class="headerlink" title="🚪 Spring Boot 入门"></a>🚪 Spring Boot 入门</h1><hr>
<h2 id="1-Spring-Boot-简介"><a href="#1-Spring-Boot-简介" class="headerlink" title="1. Spring Boot 简介"></a>1. Spring Boot 简介</h2><p>开发一个web应用，从最初开始接触Servlet结合Tomcat, 跑出一个Hello Wolrld程序，是要经历特别多的步骤；后来就用了框架Struts，再后来是SpringMVC，到了现在的SpringBoot，过一两年又会有其他web框架出现；</p>
<p>言归正传，什么是SpringBoot呢，就是一个javaweb的开发框架，和SpringMVC类似，对比其他javaweb框架的好处，官方说是简化开发，**约定大于配置，  you can “just run”**，能迅速的开发web应用，几行代码开发一个http接口。</p>
<p>所有的技术框架的发展似乎都遵循了一条主线规律：从一个复杂应用场景 衍生 一种规范框架，人们只需要进行各种配置而不需要自己去实现它，这时候强大的配置功能成了优点；发展到一定程度之后，人们根据实际生产应用情况，选取其中实用功能和设计精华，重构出一些轻量级的框架；之后为了提高开发效率，嫌弃原先的各类配置过于麻烦，于是开始提倡“约定大于配置”，进而衍生出一些一站式的解决方案。</p>
<p>这就是Java企业级应用-&gt;J2EE-&gt;spring-&gt;springboot的过程。</p>
<p>随着 Spring 不断的发展，涉及的领域越来越多，项目整合开发需要配合各种各样的文件，慢慢变得不那么易用简单，违背了最初的理念，甚至人称配置地狱。Spring Boot 正是在这样的一个背景下被抽象出来的开发框架，目的为了让大家更容易的使用 Spring 、更容易的集成各种常用的中间件、开源软件；</p>
<p>Spring Boot 基于 Spring 开发，Spirng Boot 本身并不提供 Spring 框架的核心特性以及扩展功能，只是用于快速、敏捷地开发新一代基于 Spring 框架的应用程序。也就是说，它并不是用来替代 Spring 的解决方案，而是和 Spring 框架紧密结合用于提升 Spring 开发者体验的工具。Spring Boot 以<strong>约定大于配置的核心思想</strong>，默认帮我们进行了很多设置，多数 Spring Boot 应用只需要很少的 Spring 配置。同时它集成了大量常用的第三方库配置（例如 Redis、MongoDB、Jpa、RabbitMQ、Quartz 等等），Spring Boot 应用中这些第三方库几乎可以零配置的开箱即用。</p>
<p>简单来说就是SpringBoot其实不是什么新的框架，它默认配置了很多框架的使用方式，就像maven整合了所有的jar包，spring boot整合了所有的框架 。</p>
<p>Spring Boot 出生名门，从一开始就站在一个比较高的起点，又经过这几年的发展，生态足够完善，Spring Boot 已经当之无愧成为 Java 领域最热门的技术。</p>
<p><strong>Spring Boot的主要优点：</strong></p>
<ul>
<li>为所有Spring开发者更快的入门</li>
<li><strong>开箱即用</strong>，提供各种默认配置来简化项目配置</li>
<li>内嵌式容器简化Web项目</li>
<li>没有冗余代码生成和XML配置的要求</li>
</ul>
<p><img src="https://gitee.com/veal98/images/raw/master/img/20200528210455.png"></p>
<h2 id="2-微服务介绍"><a href="#2-微服务介绍" class="headerlink" title="2. 微服务介绍"></a>2. 微服务介绍</h2><p><strong>微服务</strong>：是一种架构风格（服务微化）</p>
<p>一个应用应该是一组小型服务；可以通过 HTTP 的方式进行互通；</p>
<blockquote>
<p><strong>单体应用</strong>：ALL IN ONE</p>
<p><img src="https://gitee.com/veal98/images/raw/master/img/20200528211512.png"></p>
</blockquote>
<p><strong>微服务：每一个功能元素最终都是一个可独立替换和独立升级的软件单元：</strong></p>
<img src="https://gitee.com/veal98/images/raw/master/img/20200528211629.png"  />



<h2 id="3-环境准备"><a href="#3-环境准备" class="headerlink" title="3. 环境准备"></a>3. 环境准备</h2><p>本博客所用环境：</p>
<ul>
<li><p><strong>jdk 1.8</strong>：Spring Boot 推荐 jdk1.7 及以上；java version “1.8.0_112”</p>
</li>
<li><p><strong>maven 3.x</strong>：maven 3.3 以上版本；Apache Maven 3.3.9</p>
</li>
<li><p><strong>SpringBoot 2.3.1</strong></p>
</li>
</ul>
<p>开发工具 ：</p>
<ul>
<li><strong>IDEA 2017</strong></li>
</ul>
<h2 id="4-HelloWorld"><a href="#4-HelloWorld" class="headerlink" title="4. HelloWorld"></a>4. HelloWorld</h2><p>我们将学习如何快速的创建一个Spring Boot应用，并且实现一个简单的Http请求处理。通过这个例子对Spring Boot有一个初步的了解，并体验其结构简单、开发快速的特性。</p>
<p>💬 需求：浏览器发送 hello 请求，服务器接受请求并处理，响应Hello World 字符串。</p>
<h3 id="①-Spring-Initializer-快速创建-Spring-Boot-项目"><a href="#①-Spring-Initializer-快速创建-Spring-Boot-项目" class="headerlink" title="① Spring Initializer 快速创建 Spring Boot 项目"></a>① Spring Initializer 快速创建 Spring Boot 项目</h3><p>IDE 都支持使用 Spring 的<u>项目创建向导</u>快速创建一个 Spring Boot 项目；</p>
<img src="https://gitee.com/veal98/images/raw/master/img/20200529093821.png" style="zoom:80%;" />

<img src="https://gitee.com/veal98/images/raw/master/img/20200630222558.png" style="zoom: 67%;" />

<p>OK，然后选择我们需要的模块，向导会联网自动创建 Spring Boot 项目；</p>
<img src="https://gitee.com/veal98/images/raw/master/img/20200529093907.png" style="zoom:67%;" />

<p>🎉 默认生成的 Spring Boot 项目目录结构如下：</p>
<p><img src="https://gitee.com/veal98/images/raw/master/img/20200529094814.png"></p>
<ul>
<li><p>程序的<strong>主启动类</strong></p>
<pre class="line-numbers language-java" data-language="java"><code class="language-java"><span class="token comment">/**
 *  @SpringBootApplication 来标注一个主程序类，说明这是一个Spring Boot应用
 */</span>
<span class="token annotation punctuation">@SpringBootApplication</span>
<span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">HelloWorldMainApplication</span> <span class="token punctuation">&#123;</span>

    <span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">void</span> <span class="token function">main</span><span class="token punctuation">(</span><span class="token class-name">String</span><span class="token punctuation">[</span><span class="token punctuation">]</span> args<span class="token punctuation">)</span> <span class="token punctuation">&#123;</span>

        <span class="token comment">// 启动 Spring 应用</span>
        <span class="token class-name">SpringApplication</span><span class="token punctuation">.</span><span class="token function">run</span><span class="token punctuation">(</span><span class="token class-name">HelloWorldMainApplication</span><span class="token punctuation">.</span><span class="token keyword">class</span><span class="token punctuation">,</span>args<span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">&#125;</span>
<span class="token punctuation">&#125;</span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre></li>
<li><p>一个 测试类</p>
</li>
<li><p>一个<code> pom.xml</code></p>
</li>
<li><p><code>resources</code> 文件夹：</p>
<ul>
<li><code>static</code>：保存所有的静态资源； js / css  / images；</li>
<li><code>templates</code>：保存所有的模板页面。（Spring Boot 默认 jar 包使用嵌入式的 Tomcat，<u>默认不支持JSP页面</u>），可以使用模板引擎（freemarker、thymeleaf）；</li>
<li><code>application.properties</code>：Spring Boot 应用的配置文件，可以修改一些默认设置；</li>
</ul>
</li>
</ul>
<h3 id="②-pom-xml"><a href="#②-pom-xml" class="headerlink" title="② pom.xml"></a>② pom.xml</h3><p>打开 <code>pom.xml</code>，看看 Spring Boot 项目的依赖：</p>
<pre class="line-numbers language-xml" data-language="xml"><code class="language-xml"><span class="token comment">&lt;!-- 父依赖 --></span>
   <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>parent</span><span class="token punctuation">></span></span>
       <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>groupId</span><span class="token punctuation">></span></span>org.springframework.boot<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>groupId</span><span class="token punctuation">></span></span>
       <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>artifactId</span><span class="token punctuation">></span></span>spring-boot-starter-parent<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>artifactId</span><span class="token punctuation">></span></span>
       <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>version</span><span class="token punctuation">></span></span>2.3.1.RELEASE<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>version</span><span class="token punctuation">></span></span>
       <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>relativePath</span><span class="token punctuation">/></span></span> <span class="token comment">&lt;!-- lookup parent from repository --></span>
   <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>parent</span><span class="token punctuation">></span></span>
   <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>groupId</span><span class="token punctuation">></span></span>com.smallbeef<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>groupId</span><span class="token punctuation">></span></span>
   <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>artifactId</span><span class="token punctuation">></span></span>springboot_helloworld<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>artifactId</span><span class="token punctuation">></span></span>
   <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>version</span><span class="token punctuation">></span></span>0.0.1-SNAPSHOT<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>version</span><span class="token punctuation">></span></span>
   <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>name</span><span class="token punctuation">></span></span>springboot_helloworld<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>name</span><span class="token punctuation">></span></span>
   <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>description</span><span class="token punctuation">></span></span>Demo project for Spring Boot<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>description</span><span class="token punctuation">></span></span>

   <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>properties</span><span class="token punctuation">></span></span>
       <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>java.version</span><span class="token punctuation">></span></span>1.8<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>java.version</span><span class="token punctuation">></span></span>
   <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>properties</span><span class="token punctuation">></span></span>

   <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>dependencies</span><span class="token punctuation">></span></span>
       <span class="token comment">&lt;!-- web场景启动器 --></span>
       <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>dependency</span><span class="token punctuation">></span></span>
           <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>groupId</span><span class="token punctuation">></span></span>org.springframework.boot<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>groupId</span><span class="token punctuation">></span></span>
           <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>artifactId</span><span class="token punctuation">></span></span>spring-boot-starter-web<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>artifactId</span><span class="token punctuation">></span></span>
       <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>dependency</span><span class="token punctuation">></span></span>
       
	<span class="token comment">&lt;!-- springboot单元测试 --></span>
       <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>dependency</span><span class="token punctuation">></span></span>
           <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>groupId</span><span class="token punctuation">></span></span>org.springframework.boot<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>groupId</span><span class="token punctuation">></span></span>
           <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>artifactId</span><span class="token punctuation">></span></span>spring-boot-starter-test<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>artifactId</span><span class="token punctuation">></span></span>
           <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>scope</span><span class="token punctuation">></span></span>test<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>scope</span><span class="token punctuation">></span></span>
           <span class="token comment">&lt;!-- 剔除依赖 --></span>
           <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>exclusions</span><span class="token punctuation">></span></span>
               <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>exclusion</span><span class="token punctuation">></span></span>
                   <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>groupId</span><span class="token punctuation">></span></span>org.junit.vintage<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>groupId</span><span class="token punctuation">></span></span>
                   <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>artifactId</span><span class="token punctuation">></span></span>junit-vintage-engine<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>artifactId</span><span class="token punctuation">></span></span>
               <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>exclusion</span><span class="token punctuation">></span></span>
           <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>exclusions</span><span class="token punctuation">></span></span>
       <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>dependency</span><span class="token punctuation">></span></span>
   <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>dependencies</span><span class="token punctuation">></span></span>

   <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>build</span><span class="token punctuation">></span></span>
       <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>plugins</span><span class="token punctuation">></span></span>
           <span class="token comment">&lt;!-- 打包插件 --></span>
           <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>plugin</span><span class="token punctuation">></span></span>
               <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>groupId</span><span class="token punctuation">></span></span>org.springframework.boot<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>groupId</span><span class="token punctuation">></span></span>
               <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>artifactId</span><span class="token punctuation">></span></span>spring-boot-maven-plugin<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>artifactId</span><span class="token punctuation">></span></span>
           <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>plugin</span><span class="token punctuation">></span></span>
       <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>plugins</span><span class="token punctuation">></span></span>
   <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>build</span><span class="token punctuation">></span></span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>

<h3 id="③-编写-Controller"><a href="#③-编写-Controller" class="headerlink" title="③ 编写 Controller"></a>③ 编写 Controller</h3><p>在主程序的同级目录下，新建一个 <code>controller </code>包，在包中新建一个 <code>HelloController</code> 类</p>
<pre class="line-numbers language-java" data-language="java"><code class="language-java"><span class="token annotation punctuation">@Controller</span>
<span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">HelloController</span> <span class="token punctuation">&#123;</span>

    <span class="token annotation punctuation">@ResponseBody</span>
    <span class="token annotation punctuation">@RequestMapping</span><span class="token punctuation">(</span><span class="token string">"/hello"</span><span class="token punctuation">)</span>
    <span class="token keyword">public</span> <span class="token class-name">String</span> <span class="token function">hello</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">&#123;</span>
        <span class="token keyword">return</span> <span class="token string">"Hello World!"</span><span class="token punctuation">;</span>
    <span class="token punctuation">&#125;</span>
<span class="token punctuation">&#125;</span>
<span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>

<blockquote>
<p>@ ResponseBody 直接将返回值作为字符串返回给浏览器，而不是作为一个 jsp 界面</p>
<p>⭐ <u>@Controller + @ResponseBody = @<strong>RestController</strong></u>。所以也可这样写：</p>
<pre class="line-numbers language-java" data-language="java"><code class="language-java"><span class="token annotation punctuation">@RestController</span>
<span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">HelloController</span> <span class="token punctuation">&#123;</span>

    <span class="token annotation punctuation">@RequestMapping</span><span class="token punctuation">(</span><span class="token string">"/hello"</span><span class="token punctuation">)</span>
    <span class="token keyword">public</span> <span class="token class-name">String</span> <span class="token function">hello</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">&#123;</span>
        <span class="token keyword">return</span> <span class="token string">"Hello World!"</span><span class="token punctuation">;</span>
    <span class="token punctuation">&#125;</span>
<span class="token punctuation">&#125;</span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>


</blockquote>
<h3 id="④-运行-main-函数测试"><a href="#④-运行-main-函数测试" class="headerlink" title="④ 运行 main 函数测试"></a>④ 运行 main 函数测试</h3><p>直接运行 Main 函数即可，<a target="_blank" rel="noopener" href="http://localhost:8080/hello">http://localhost:8080/hello</a></p>
<blockquote>
<p>😊 简单几步，就完成了一个 web 接口的开发，SpringBoot 就是这么简单。所以我们常用它来建立我们的微服务项目！</p>
</blockquote>
<h3 id="⑥-将项目打成-jar-包"><a href="#⑥-将项目打成-jar-包" class="headerlink" title="⑥ 将项目打成 jar 包"></a>⑥ 将项目打成 jar 包</h3><p>无须在目标服务器安装 Tomcat 环境等等，该 jar 包可直接运行。</p>
<pre class="line-numbers language-xml" data-language="xml"><code class="language-xml"><span class="token comment">&lt;!-- 这个插件，可以将应用打包成一个可执行的jar包；--></span>
   <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>build</span><span class="token punctuation">></span></span>
       <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>plugins</span><span class="token punctuation">></span></span>
           <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>plugin</span><span class="token punctuation">></span></span>
               <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>groupId</span><span class="token punctuation">></span></span>org.springframework.boot<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>groupId</span><span class="token punctuation">></span></span>
               <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>artifactId</span><span class="token punctuation">></span></span>spring-boot-maven-plugin<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>artifactId</span><span class="token punctuation">></span></span>
           <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>plugin</span><span class="token punctuation">></span></span>
       <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>plugins</span><span class="token punctuation">></span></span>
   <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>build</span><span class="token punctuation">></span></span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>

<p>打包：</p>
<p><img src="https://gitee.com/veal98/images/raw/master/img/20200528220845.png"></p>
<p>成功打包后该 <code>jar</code> 包会放在 <code>target </code>文件夹下：</p>
<p><img src="https://gitee.com/veal98/images/raw/master/img/20200528220933.png"></p>
<p>直接使用 <code>java -jar 包名</code> 的命令即可执行该 jar 包。</p>
<p>首先，打开命令行 cd 到该 <code>jar </code>包所在文件夹，然后运行以下命令：</p>
<pre class="line-numbers language-powershell" data-language="powershell"><code class="language-powershell">java <span class="token operator">-</span>jar spring_boot<span class="token operator">-</span>01<span class="token operator">-</span>helloworld<span class="token operator">-</span>1<span class="token punctuation">.</span>0<span class="token operator">-</span>SNAPSHOT<span class="token punctuation">.</span>jar<span aria-hidden="true" class="line-numbers-rows"><span></span></span></code></pre>

<h2 id="5-Hello-World探究"><a href="#5-Hello-World探究" class="headerlink" title="5. Hello World探究"></a>5. Hello World探究</h2><h3 id="①-POM-文件"><a href="#①-POM-文件" class="headerlink" title="① POM 文件"></a>① POM 文件</h3><h4 id="Ⅰ-父项目-父依赖"><a href="#Ⅰ-父项目-父依赖" class="headerlink" title="Ⅰ 父项目 / 父依赖"></a>Ⅰ 父项目 / 父依赖</h4><p><code>pom.xml</code> 主要是依赖一个父项目，主要管理项目的资源过滤及插件：</p>
<pre class="line-numbers language-xml" data-language="xml"><code class="language-xml"><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>parent</span><span class="token punctuation">></span></span>
    <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>groupId</span><span class="token punctuation">></span></span>org.springframework.boot<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>groupId</span><span class="token punctuation">></span></span>
    <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>artifactId</span><span class="token punctuation">></span></span>spring-boot-starter-parent<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>artifactId</span><span class="token punctuation">></span></span>
    <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>version</span><span class="token punctuation">></span></span>2.3.1.RELEASE<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>version</span><span class="token punctuation">></span></span>
    <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>relativePath</span><span class="token punctuation">/></span></span> <span class="token comment">&lt;!-- lookup parent from repository --></span>
<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>parent</span><span class="token punctuation">></span></span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>

<p><code>Ctrl  + 右键</code>点进 <code>spring-boot-starter-parent</code>，发现还有一个父依赖： 👇</p>
<pre class="line-numbers language-xml" data-language="xml"><code class="language-xml"><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>parent</span><span class="token punctuation">></span></span>
    <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>groupId</span><span class="token punctuation">></span></span>org.springframework.boot<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>groupId</span><span class="token punctuation">></span></span>
    <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>artifactId</span><span class="token punctuation">></span></span>spring-boot-dependencies<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>artifactId</span><span class="token punctuation">></span></span>
    <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>version</span><span class="token punctuation">></span></span>2.3.1.RELEASE<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>version</span><span class="token punctuation">></span></span>
<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>parent</span><span class="token punctuation">></span></span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span></span></code></pre>

<p>这里才是真正管理 SpringBoot 应用里面所有依赖版本的地方，SpringBoot 的版本控制中心。</p>
<p>以后我们导入依赖默认是不需要写版本的。（但是没有在 dependencies 里面管理的依赖需要声明版本号）</p>
<h4 id="Ⅱ-启动器-spring-boot-starter"><a href="#Ⅱ-启动器-spring-boot-starter" class="headerlink" title="Ⅱ 启动器 spring-boot-starter"></a>Ⅱ 启动器 spring-boot-starter</h4><pre class="line-numbers language-xml" data-language="xml"><code class="language-xml"><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>dependency</span><span class="token punctuation">></span></span>
    <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>groupId</span><span class="token punctuation">></span></span>org.springframework.boot<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>groupId</span><span class="token punctuation">></span></span>
    <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>artifactId</span><span class="token punctuation">></span></span>spring-boot-starter-web<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>artifactId</span><span class="token punctuation">></span></span>
<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>dependency</span><span class="token punctuation">></span></span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span></span></code></pre>

<ul>
<li><p><code>spring-boot-starter-xxx</code>：<strong>spring-boot 场景启动器</strong>；</p>
</li>
<li><p><code>spring-boot-starter-web</code>：帮我们导入了 web 模块正常运行所依赖的组件：</p>
<p><img src="https://gitee.com/veal98/images/raw/master/img/20200528221854.png"></p>
</li>
</ul>
<p>⭐ Spring Boot将所有的功能场景都抽取出来，做成一个个的 starter（启动器），只需要在项目里面引入这些 starter ，相关场景的所有依赖都会导入进来。要用什么功能就导入什么场景的启动器</p>
<p><img src="https://gitee.com/veal98/images/raw/master/img/20200528222416.png"></p>
<h3 id="②-主启动类-主程序类"><a href="#②-主启动类-主程序类" class="headerlink" title="② 主启动类/主程序类"></a>② 主启动类/主程序类</h3><pre class="line-numbers language-java" data-language="java"><code class="language-java"><span class="token comment">/**
 *  @SpringBootApplication 来标注一个主程序类，说明这是一个Spring Boot应用
 */</span>
<span class="token annotation punctuation">@SpringBootApplication</span>
<span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">HelloWorldMainApplication</span> <span class="token punctuation">&#123;</span>

    <span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">void</span> <span class="token function">main</span><span class="token punctuation">(</span><span class="token class-name">String</span><span class="token punctuation">[</span><span class="token punctuation">]</span> args<span class="token punctuation">)</span><span class="token punctuation">&#123;</span>
        <span class="token class-name">SpringApplication</span><span class="token punctuation">.</span><span class="token function">run</span><span class="token punctuation">(</span><span class="token class-name">HelloWorldMainApplication</span><span class="token punctuation">.</span><span class="token keyword">class</span><span class="token punctuation">,</span>args<span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">&#125;</span>
<span class="token punctuation">&#125;</span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>

<h4 id="Ⅰ-SpringBootApplication"><a href="#Ⅰ-SpringBootApplication" class="headerlink" title="Ⅰ @SpringBootApplication"></a>Ⅰ @SpringBootApplication</h4><p>⭐ <code>@SpringBootApplication</code>（Spring Boot应用）：<strong>标注在某个类上说明这个类是 SpringBoot 的主程序类</strong>，SpringBoot 就应该运行这个类的 <code>main </code>方法来启动 SpringBoot 应用；</p>
<p>📑 该注解源码如下：</p>
<pre class="line-numbers language-java" data-language="java"><code class="language-java"><span class="token annotation punctuation">@SpringBootConfiguration</span>
<span class="token annotation punctuation">@EnableAutoConfiguration</span>
<span class="token annotation punctuation">@ComponentScan</span><span class="token punctuation">(</span>
    excludeFilters <span class="token operator">=</span> <span class="token punctuation">&#123;</span><span class="token annotation punctuation">@Filter</span><span class="token punctuation">(</span>
    type <span class="token operator">=</span> <span class="token class-name">FilterType</span><span class="token punctuation">.</span>CUSTOM<span class="token punctuation">,</span>
    classes <span class="token operator">=</span> <span class="token punctuation">&#123;</span><span class="token class-name">TypeExcludeFilter</span><span class="token punctuation">.</span><span class="token keyword">class</span><span class="token punctuation">&#125;</span>
<span class="token punctuation">)</span><span class="token punctuation">,</span> <span class="token annotation punctuation">@Filter</span><span class="token punctuation">(</span>
    type <span class="token operator">=</span> <span class="token class-name">FilterType</span><span class="token punctuation">.</span>CUSTOM<span class="token punctuation">,</span>
    classes <span class="token operator">=</span> <span class="token punctuation">&#123;</span><span class="token class-name">AutoConfigurationExcludeFilter</span><span class="token punctuation">.</span><span class="token keyword">class</span><span class="token punctuation">&#125;</span>
<span class="token punctuation">)</span><span class="token punctuation">&#125;</span>
<span class="token punctuation">)</span>
<span class="token keyword">public</span> <span class="token annotation punctuation">@interface</span> <span class="token class-name">SpringBootApplication</span> <span class="token punctuation">&#123;</span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>

<p>底层由三个注解实现：</p>
<ul>
<li><code>@SpringBootConfiguration</code></li>
<li><code>@EnableAutoConfiguration</code></li>
<li><code>@ComponentScan</code></li>
</ul>
<p>接下来进行详细的解析：👇</p>
<h4 id="Ⅱ-ComponentScan"><a href="#Ⅱ-ComponentScan" class="headerlink" title="Ⅱ @ComponentScan"></a>Ⅱ @ComponentScan</h4><p>Spring 中的注解 ,它对应 XML 配置中的元素。</p>
<p>作用：<strong>自动扫描并加载符合条件的组件或者 bean ， 将这个 bean 定义加载到 IoC 容器中</strong></p>
<h4 id="Ⅲ-SpringBootConfiguration"><a href="#Ⅲ-SpringBootConfiguration" class="headerlink" title="Ⅲ @SpringBootConfiguration"></a>Ⅲ @SpringBootConfiguration</h4><p><code>@SpringBootConfiguration</code>: Spring Boot 的配置类。<strong>标注在某个类上，表示这是一个 Spring Boot 的配置类</strong>。</p>
<p>📑 该注解源码如下：</p>
<pre class="line-numbers language-java" data-language="java"><code class="language-java"><span class="token annotation punctuation">@Configuration</span>
<span class="token keyword">public</span> <span class="token annotation punctuation">@interface</span> <span class="token class-name">SpringBootConfiguration</span> <span class="token punctuation">&#123;</span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span></span></code></pre>

<p>底层是 <code>@Configuration</code>: 说明这是一个配置类（配置类就是对应 Spring 的 xml  配置文件）</p>
<p>📑 <code>@Configuration</code> 源码如下：</p>
<pre class="line-numbers language-java" data-language="java"><code class="language-java"><span class="token annotation punctuation">@Component</span>
<span class="token keyword">public</span> <span class="token annotation punctuation">@interface</span> <span class="token class-name">Configuration</span> <span class="token punctuation">&#123;</span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span></span></code></pre>

<p>里面的 <code>@Component</code> 这就说明，<strong>启动类本身也是 Spring 中的一个组件而已</strong>，负责启动应用。</p>
<h4 id="Ⅳ-EnableAutoConfiguration"><a href="#Ⅳ-EnableAutoConfiguration" class="headerlink" title="Ⅳ @EnableAutoConfiguration"></a>Ⅳ @EnableAutoConfiguration</h4><p><code>@EnableAutoConfiguration</code>：<strong>开启自动配置功能</strong>。</p>
<p>以前我们需要配置的东西，Spring Boot 帮我们自动配置；</p>
<p><code>@EnableAutoConfiguration</code>告诉 SpringBoot 开启自动配置功能，这样自动配置才能生效；</p>
<p>📑 该注解的源码如下：</p>
<pre class="line-numbers language-java" data-language="java"><code class="language-java"><span class="token annotation punctuation">@AutoConfigurationPackage</span>
<span class="token annotation punctuation">@Import</span><span class="token punctuation">(</span><span class="token punctuation">&#123;</span><span class="token class-name">AutoConfigurationImportSelector</span><span class="token punctuation">.</span><span class="token keyword">class</span><span class="token punctuation">&#125;</span><span class="token punctuation">)</span>
<span class="token keyword">public</span> <span class="token annotation punctuation">@interface</span> <span class="token class-name">EnableAutoConfiguration</span> <span class="token punctuation">&#123;</span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span></span></code></pre>

<ul>
<li><p>⭐ <code>@AutoConfigurationPackage</code><strong>：自动配置包，</strong><u>将主配置类（<code>@SpringBootApplication</code>标注的类）的所在包及下面所有子包里面的所有组件扫描到 Spring 容器中</u></p>
<p>📑 该注解的源码如下：</p>
<pre class="line-numbers language-java" data-language="java"><code class="language-java"><span class="token annotation punctuation">@Import</span><span class="token punctuation">(</span><span class="token punctuation">&#123;</span><span class="token class-name">Registrar</span><span class="token punctuation">.</span><span class="token keyword">class</span><span class="token punctuation">&#125;</span><span class="token punctuation">)</span>
<span class="token keyword">public</span> <span class="token annotation punctuation">@interface</span> <span class="token class-name">AutoConfigurationPackage</span> <span class="token punctuation">&#123;</span>
<span class="token punctuation">&#125;</span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span></span></code></pre>

<ul>
<li><p><code>@Import(&#123;Registrar.class&#125;)</code>：<code>@import</code>是 Spring 中的底层注解，给容器中导入一个组件</p>
</li>
<li><p><code>Registrar.class</code> 作用：将主启动类的所在包及包下面所有子包里面的所有组件扫描到 Spring 容器 ；</p>
</li>
</ul>
</li>
<li><p><code>@Import(&#123;AutoConfigurationImportSelector.class&#125;)</code>：给容器中导入组件。</p>
<p><code>AutoConfigurationImportSelector</code>：<strong>自动配置导入选择器</strong>。将所有需要导入的组件以全类名的方式返回；这些组件就会被添加到容器中。</p>
<p>那么它会导入哪些组件的选择器呢？📑 我们点击去这个类看源码：</p>
<p>这个类中有一个这样的方法：</p>
<pre class="line-numbers language-java" data-language="java"><code class="language-java"><span class="token comment">// 获得候选的配置</span>
<span class="token keyword">protected</span> <span class="token class-name">List</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">String</span><span class="token punctuation">></span></span> <span class="token function">getCandidateConfigurations</span><span class="token punctuation">(</span><span class="token class-name">AnnotationMetadata</span> metadata<span class="token punctuation">,</span> <span class="token class-name">AnnotationAttributes</span> attributes<span class="token punctuation">)</span> <span class="token punctuation">&#123;</span>
    <span class="token comment">// 这里的 getSpringFactoriesLoaderFactoryClass() 方法</span>
    <span class="token comment">// 返回的就是启动自动导入配置文件的注解类；EnableAutoConfiguration</span>
    <span class="token class-name">List</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">String</span><span class="token punctuation">></span></span> configurations <span class="token operator">=</span> <span class="token class-name">SpringFactoriesLoader</span><span class="token punctuation">.</span><span class="token function">loadFactoryNames</span><span class="token punctuation">(</span><span class="token keyword">this</span><span class="token punctuation">.</span><span class="token function">getSpringFactoriesLoaderFactoryClass</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">,</span> <span class="token keyword">this</span><span class="token punctuation">.</span><span class="token function">getBeanClassLoader</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token class-name">Assert</span><span class="token punctuation">.</span><span class="token function">notEmpty</span><span class="token punctuation">(</span>configurations<span class="token punctuation">,</span> <span class="token string">"No auto configuration classes found in META-INF/spring.factories. If you are using a custom packaging, make sure that file is correct."</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token keyword">return</span> configurations<span class="token punctuation">;</span>
<span class="token punctuation">&#125;</span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>

<p>这个方法又调用了  <code>SpringFactoriesLoader </code> 类的静态方法，我们进入<code>SpringFactoriesLoader</code> 类 <code>loadFactoryNames()</code> 方法：</p>
<pre class="line-numbers language-java" data-language="java"><code class="language-java"><span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token class-name">List</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">String</span><span class="token punctuation">></span></span> <span class="token function">loadFactoryNames</span><span class="token punctuation">(</span><span class="token class-name">Class</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token operator">?</span><span class="token punctuation">></span></span> factoryClass<span class="token punctuation">,</span> <span class="token annotation punctuation">@Nullable</span> <span class="token class-name">ClassLoader</span> classLoader<span class="token punctuation">)</span> <span class="token punctuation">&#123;</span>
    <span class="token class-name">String</span> factoryClassName <span class="token operator">=</span> factoryClass<span class="token punctuation">.</span><span class="token function">getName</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token comment">// 这里它又调用了 loadSpringFactories 方法</span>
    <span class="token keyword">return</span> <span class="token punctuation">(</span><span class="token class-name">List</span><span class="token punctuation">)</span><span class="token function">loadSpringFactories</span><span class="token punctuation">(</span>classLoader<span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">getOrDefault</span><span class="token punctuation">(</span>factoryClassName<span class="token punctuation">,</span> <span class="token class-name">Collections</span><span class="token punctuation">.</span><span class="token function">emptyList</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">&#125;</span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span></span></code></pre>

<p>我们继续点击查看 <code>loadSpringFactories </code>方法：</p>
<pre class="line-numbers language-java" data-language="java"><code class="language-java"><span class="token keyword">private</span> <span class="token keyword">static</span> <span class="token class-name">Map</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">String</span><span class="token punctuation">,</span> <span class="token class-name">List</span><span class="token punctuation">&lt;</span><span class="token class-name">String</span><span class="token punctuation">></span><span class="token punctuation">></span></span> <span class="token function">loadSpringFactories</span><span class="token punctuation">(</span><span class="token annotation punctuation">@Nullable</span> <span class="token class-name">ClassLoader</span> classLoader<span class="token punctuation">)</span> <span class="token punctuation">&#123;</span>
    <span class="token comment">// 获得classLoader ， 我们返回可以看到这里得到的就是EnableAutoConfiguration标注的类本身</span>
    <span class="token class-name">MultiValueMap</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">String</span><span class="token punctuation">,</span> <span class="token class-name">String</span><span class="token punctuation">></span></span> result <span class="token operator">=</span> <span class="token punctuation">(</span><span class="token class-name">MultiValueMap</span><span class="token punctuation">)</span>cache<span class="token punctuation">.</span><span class="token function">get</span><span class="token punctuation">(</span>classLoader<span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token keyword">if</span> <span class="token punctuation">(</span>result <span class="token operator">!=</span> <span class="token keyword">null</span><span class="token punctuation">)</span> <span class="token punctuation">&#123;</span>
        <span class="token keyword">return</span> result<span class="token punctuation">;</span>
    <span class="token punctuation">&#125;</span> <span class="token keyword">else</span> <span class="token punctuation">&#123;</span>
        <span class="token keyword">try</span> <span class="token punctuation">&#123;</span>
            <span class="token comment">//去获取一个资源 "META-INF/spring.factories"</span>
            <span class="token class-name">Enumeration</span><span class="token generics"><span class="token punctuation">&lt;</span>URL<span class="token punctuation">></span></span> urls <span class="token operator">=</span> classLoader <span class="token operator">!=</span> <span class="token keyword">null</span> <span class="token operator">?</span> classLoader<span class="token punctuation">.</span><span class="token function">getResources</span><span class="token punctuation">(</span><span class="token string">"META-INF/spring.factories"</span><span class="token punctuation">)</span> <span class="token operator">:</span> <span class="token class-name">ClassLoader</span><span class="token punctuation">.</span><span class="token function">getSystemResources</span><span class="token punctuation">(</span><span class="token string">"META-INF/spring.factories"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
            <span class="token class-name">LinkedMultiValueMap</span> result <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">LinkedMultiValueMap</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

            <span class="token comment">//将读取到的资源遍历，封装成为一个Properties</span>
            <span class="token keyword">while</span><span class="token punctuation">(</span>urls<span class="token punctuation">.</span><span class="token function">hasMoreElements</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">&#123;</span>
                <span class="token class-name">URL</span> url <span class="token operator">=</span> <span class="token punctuation">(</span>URL<span class="token punctuation">)</span>urls<span class="token punctuation">.</span><span class="token function">nextElement</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
                <span class="token class-name">UrlResource</span> resource <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">UrlResource</span><span class="token punctuation">(</span>url<span class="token punctuation">)</span><span class="token punctuation">;</span>
                <span class="token class-name">Properties</span> properties <span class="token operator">=</span> <span class="token class-name">PropertiesLoaderUtils</span><span class="token punctuation">.</span><span class="token function">loadProperties</span><span class="token punctuation">(</span>resource<span class="token punctuation">)</span><span class="token punctuation">;</span>
                <span class="token class-name">Iterator</span> var6 <span class="token operator">=</span> properties<span class="token punctuation">.</span><span class="token function">entrySet</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">iterator</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

                <span class="token keyword">while</span><span class="token punctuation">(</span>var6<span class="token punctuation">.</span><span class="token function">hasNext</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">&#123;</span>
                    <span class="token class-name">Entry</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token operator">?</span><span class="token punctuation">,</span> <span class="token operator">?</span><span class="token punctuation">></span></span> entry <span class="token operator">=</span> <span class="token punctuation">(</span><span class="token class-name">Entry</span><span class="token punctuation">)</span>var6<span class="token punctuation">.</span><span class="token function">next</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
                    <span class="token class-name">String</span> factoryClassName <span class="token operator">=</span> <span class="token punctuation">(</span><span class="token punctuation">(</span><span class="token class-name">String</span><span class="token punctuation">)</span>entry<span class="token punctuation">.</span><span class="token function">getKey</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">trim</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
                    <span class="token class-name">String</span><span class="token punctuation">[</span><span class="token punctuation">]</span> var9 <span class="token operator">=</span> <span class="token class-name">StringUtils</span><span class="token punctuation">.</span><span class="token function">commaDelimitedListToStringArray</span><span class="token punctuation">(</span><span class="token punctuation">(</span><span class="token class-name">String</span><span class="token punctuation">)</span>entry<span class="token punctuation">.</span><span class="token function">getValue</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
                    <span class="token keyword">int</span> var10 <span class="token operator">=</span> var9<span class="token punctuation">.</span>length<span class="token punctuation">;</span>

                    <span class="token keyword">for</span><span class="token punctuation">(</span><span class="token keyword">int</span> var11 <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">;</span> var11 <span class="token operator">&lt;</span> var10<span class="token punctuation">;</span> <span class="token operator">++</span>var11<span class="token punctuation">)</span> <span class="token punctuation">&#123;</span>
                        <span class="token class-name">String</span> factoryName <span class="token operator">=</span> var9<span class="token punctuation">[</span>var11<span class="token punctuation">]</span><span class="token punctuation">;</span>
                        result<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span>factoryClassName<span class="token punctuation">,</span> factoryName<span class="token punctuation">.</span><span class="token function">trim</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
                    <span class="token punctuation">&#125;</span>
                <span class="token punctuation">&#125;</span>
            <span class="token punctuation">&#125;</span>

            cache<span class="token punctuation">.</span><span class="token function">put</span><span class="token punctuation">(</span>classLoader<span class="token punctuation">,</span> result<span class="token punctuation">)</span><span class="token punctuation">;</span>
            <span class="token keyword">return</span> result<span class="token punctuation">;</span>
        <span class="token punctuation">&#125;</span> <span class="token keyword">catch</span> <span class="token punctuation">(</span><span class="token class-name">IOException</span> var13<span class="token punctuation">)</span> <span class="token punctuation">&#123;</span>
            <span class="token keyword">throw</span> <span class="token keyword">new</span> <span class="token class-name">IllegalArgumentException</span><span class="token punctuation">(</span><span class="token string">"Unable to load factories from location [META-INF/spring.factories]"</span><span class="token punctuation">,</span> var13<span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token punctuation">&#125;</span>
    <span class="token punctuation">&#125;</span>
<span class="token punctuation">&#125;</span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre></li>
</ul>
<h4 id="Ⅴ-spring-factories"><a href="#Ⅴ-spring-factories" class="headerlink" title="Ⅴ spring.factories"></a>Ⅴ spring.factories</h4><p>⭐ 在上面这段源码中，我们发现了一个多次出现的文件 <code>spring.factories</code>，在 <u>External Libraries</u> 中找到它：</p>
<img src="https://gitee.com/veal98/images/raw/master/img/20200701105523.png" style="zoom:80%;" /> 

<p>其中包含了很多自动配置的文件（自动配置类 <code>xxxAutoConfiguration</code>），这就是<strong>自动配置的根源所在</strong>！</p>
<p><img src="https://gitee.com/veal98/images/raw/master/img/20200701105548.png"></p>
<p>我们在上面的自动配置类随便找一个打开看看，比如 ：<code>WebMvcAutoConfiguration</code></p>
<p><img src="https://gitee.com/veal98/images/raw/master/img/20200701105838.png"></p>
<p>可以看到这些一个个的都是JavaConfig 配置类，而且都注入了一些 Bean。</p>
<p>⭐ 所以，自动配置真正实现是从 classpath 中搜寻所有的 <code>META-INF/spring.factories</code> 配置文件 ，并将其中对应的  <code>org.springframework.boot.autoconfigure.</code> 包下的配置项，通过<strong>反射</strong>实例化为对应标注了 <code>@Configuration</code> 的 JavaConfig 形式的 IoC 容器配置类 ， 然后将这些都汇总成为一个实例并加载到 IoC 容器中。</p>
<br>

<p>🚩 小结：</p>
<ul>
<li><u>Spring Boot 在启动的时候从类路径下的 <code>META-INF/spring.factories</code> 中获取 <code>EnableAutoConfiguration </code>指定的值，将这些值作为自动配置类导入到容器中，自动配置类就生效，帮我们进行自动配置工作</u>。以前我们需要自己配置的东西，自动配置类都帮我们配置好了；</li>
<li>J2EE 的整体整合解决方案和自动配置都在 <code>spring-boot-autoconfigure-2.3.1.RELEASE.jar</code>，它会给容器中导入非常多的自动配置类 （<code>xxxAutoConfiguration</code>）, 就是给容器中导入这个场景需要的所有组件 ， 并配置好这些组件 ；</li>
<li>有了自动配置类，免去了我们手动编写配置注入功能组件等的工作。</li>
</ul>
<blockquote>
<p>😊 现在大概的对 SpringBoot 的自动配置原理有所了解了，后面我们还会深化一次。</p>
</blockquote>
<h3 id="③-SpringApplication"><a href="#③-SpringApplication" class="headerlink" title="③ SpringApplication"></a>③ SpringApplication</h3><p>显然，<code>main</code> 不仅仅是运行了一个方法，而是开启了一个服务</p>
<pre class="line-numbers language-java" data-language="java"><code class="language-java"><span class="token annotation punctuation">@SpringBootApplication</span>
<span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">SpringbootHelloworldApplication</span> <span class="token punctuation">&#123;</span>

    <span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">void</span> <span class="token function">main</span><span class="token punctuation">(</span><span class="token class-name">String</span><span class="token punctuation">[</span><span class="token punctuation">]</span> args<span class="token punctuation">)</span> <span class="token punctuation">&#123;</span>
        <span class="token class-name">SpringApplication</span><span class="token punctuation">.</span><span class="token function">run</span><span class="token punctuation">(</span><span class="token class-name">SpringbootHelloworldApplication</span><span class="token punctuation">.</span><span class="token keyword">class</span><span class="token punctuation">,</span> args<span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">&#125;</span>

<span class="token punctuation">&#125;</span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>

<p><strong>SpringApplication.run 分析</strong>：该方法主要分两部分，一部分是 <code>SpringApplication</code> 的实例化，二是 <code>run</code> 方法的执行；</p>
<h4 id="Ⅰ-SpringApplication"><a href="#Ⅰ-SpringApplication" class="headerlink" title="Ⅰ SpringApplication"></a>Ⅰ SpringApplication</h4><p>📑 该类源码如下：</p>
<pre class="line-numbers language-java" data-language="java"><code class="language-java"><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">SpringApplication</span> <span class="token punctuation">&#123;</span>
    <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>
    <span class="token keyword">private</span> <span class="token class-name">List</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">ApplicationContextInitializer</span><span class="token punctuation">&lt;</span><span class="token operator">?</span><span class="token punctuation">></span><span class="token punctuation">></span></span> initializers<span class="token punctuation">;</span>
    <span class="token keyword">private</span> <span class="token class-name">List</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">ApplicationListener</span><span class="token punctuation">&lt;</span><span class="token operator">?</span><span class="token punctuation">></span><span class="token punctuation">></span></span> listeners<span class="token punctuation">;</span>
    <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>
    <span class="token keyword">public</span> <span class="token class-name">SpringApplication</span><span class="token punctuation">(</span><span class="token class-name">ResourceLoader</span> resourceLoader<span class="token punctuation">,</span> <span class="token class-name">Class</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token operator">?</span><span class="token punctuation">></span></span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span> primarySources<span class="token punctuation">)</span> <span class="token punctuation">&#123;</span>
        <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>
        <span class="token keyword">this</span><span class="token punctuation">.</span>webApplicationType <span class="token operator">=</span> <span class="token class-name">WebApplicationType</span><span class="token punctuation">.</span><span class="token function">deduceFromClasspath</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
   		<span class="token keyword">this</span><span class="token punctuation">.</span><span class="token function">setInitializers</span><span class="token punctuation">(</span><span class="token keyword">this</span><span class="token punctuation">.</span><span class="token function">getSpringFactoriesInstances</span><span class="token punctuation">(</span>
            						<span class="token class-name">ApplicationContextInitializer</span><span class="token punctuation">.</span><span class="token keyword">class</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token keyword">this</span><span class="token punctuation">.</span><span class="token function">setListeners</span><span class="token punctuation">(</span><span class="token keyword">this</span><span class="token punctuation">.</span><span class="token function">getSpringFactoriesInstances</span><span class="token punctuation">(</span><span class="token class-name">ApplicationListener</span><span class="token punctuation">.</span><span class="token keyword">class</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token keyword">this</span><span class="token punctuation">.</span>mainApplicationClass <span class="token operator">=</span> <span class="token keyword">this</span><span class="token punctuation">.</span><span class="token function">deduceMainApplicationClass</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">&#125;</span>  
  	<span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>
<span class="token punctuation">&#125;</span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>

<p>这个类主要做了以下四件事情：</p>
<ul>
<li><p>推断应用的类型是普通的项目还是 Web 项目</p>
</li>
<li><p>查找并加载所有可用初始化器 ， 设置到 <code>initializers </code>属性中</p>
</li>
<li><p>找出所有的应用程序监听器，设置到 <code>listeners</code> 属性中</p>
</li>
<li><p>推断并设置 <code>main</code> 方法的定义类，找到运行的主类</p>
</li>
</ul>
<h4 id="Ⅱ-run-方法流程分析"><a href="#Ⅱ-run-方法流程分析" class="headerlink" title="Ⅱ  run 方法流程分析"></a>Ⅱ  run 方法流程分析</h4><blockquote>
<p>🔗 图片来源狂神说公众号</p>
</blockquote>
<p><img src="https://gitee.com/veal98/images/raw/master/img/20200701111258.png"></p>
<h2 id="📚-References"><a href="#📚-References" class="headerlink" title="📚 References"></a>📚 References</h2><ul>
<li><p><a target="_blank" rel="noopener" href="https://www.bilibili.com/video/BV1Et411Y7tQ">视频 - SpringBoot_权威教程_雷丰阳_尚硅谷</a></p>
</li>
<li><p><a target="_blank" rel="noopener" href="https://mp.weixin.qq.com/mp/homepage?__biz=Mzg2NTAzMTExNg==&hid=1&sn=3247dca1433a891523d9e4176c90c499">狂神说 SpringBoot</a></p>
</li>
</ul>

                
            </div>
            <hr/>

            

    <div class="reprint" id="reprint-statement">
        
            <div class="reprint__author">
                <span class="reprint-meta" style="font-weight: bold;">
                    <i class="fas fa-user">
                        文章作者:
                    </i>
                </span>
                <span class="reprint-info">
                    <a href="/about" rel="external nofollow noreferrer">Gtwff</a>
                </span>
            </div>
            <div class="reprint__type">
                <span class="reprint-meta" style="font-weight: bold;">
                    <i class="fas fa-link">
                        文章链接:
                    </i>
                </span>
                <span class="reprint-info">
                    <a href="https://kuangty.gitee.io/2022/02/19/SpringBoot/1-SpringBoot%E5%85%A5%E9%97%A8/">https://kuangty.gitee.io/2022/02/19/SpringBoot/1-SpringBoot%E5%85%A5%E9%97%A8/</a>
                </span>
            </div>
            <div class="reprint__notice">
                <span class="reprint-meta" style="font-weight: bold;">
                    <i class="fas fa-copyright">
                        版权声明:
                    </i>
                </span>
                <span class="reprint-info">
                    本博客所有文章除特別声明外，均采用
                    <a href="https://creativecommons.org/licenses/by/4.0/deed.zh" rel="external nofollow noreferrer" target="_blank">CC BY 4.0</a>
                    许可协议。转载请注明来源
                    <a href="/about" target="_blank">Gtwff</a>
                    !
                </span>
            </div>
        
    </div>

    <script async defer>
      document.addEventListener("copy", function (e) {
        let toastHTML = '<span>复制成功，请遵循本文的转载规则</span><button class="btn-flat toast-action" onclick="navToReprintStatement()" style="font-size: smaller">查看</a>';
        M.toast({html: toastHTML})
      });

      function navToReprintStatement() {
        $("html, body").animate({scrollTop: $("#reprint-statement").offset().top - 80}, 800);
      }
    </script>



            <div class="tag_share" style="display: block;">
                <div class="post-meta__tag-list" style="display: inline-block;">
                    
                        <div class="article-tag">
                            
                                <a href="/tags/Spring-Boot-%E5%85%A5%E9%97%A8/">
                                    <span class="chip bg-color">Spring Boot 入门</span>
                                </a>
                            
                        </div>
                    
                </div>
                <div class="post_share" style="zoom: 80%; width: fit-content; display: inline-block; float: right; margin: -0.15rem 0;">
                    <link rel="stylesheet" type="text/css" href="/libs/share/css/share.min.css">
<div id="article-share">

    
    <div class="social-share" data-sites="twitter,facebook,google,qq,qzone,wechat,weibo,douban,linkedin" data-wechat-qrcode-helper="<p>微信扫一扫即可分享！</p>"></div>
    <script src="/libs/share/js/social-share.min.js"></script>
    

    

</div>

                </div>
            </div>
            
                <style>
    #reward {
        margin: 40px 0;
        text-align: center;
    }

    #reward .reward-link {
        font-size: 1.4rem;
        line-height: 38px;
    }

    #reward .btn-floating:hover {
        box-shadow: 0 6px 12px rgba(0, 0, 0, 0.2), 0 5px 15px rgba(0, 0, 0, 0.2);
    }

    #rewardModal {
        width: 320px;
        height: 350px;
    }

    #rewardModal .reward-title {
        margin: 15px auto;
        padding-bottom: 5px;
    }

    #rewardModal .modal-content {
        padding: 10px;
    }

    #rewardModal .close {
        position: absolute;
        right: 15px;
        top: 15px;
        color: rgba(0, 0, 0, 0.5);
        font-size: 1.3rem;
        line-height: 20px;
        cursor: pointer;
    }

    #rewardModal .close:hover {
        color: #ef5350;
        transform: scale(1.3);
        -moz-transform:scale(1.3);
        -webkit-transform:scale(1.3);
        -o-transform:scale(1.3);
    }

    #rewardModal .reward-tabs {
        margin: 0 auto;
        width: 210px;
    }

    .reward-tabs .tabs {
        height: 38px;
        margin: 10px auto;
        padding-left: 0;
    }

    .reward-content ul {
        padding-left: 0 !important;
    }

    .reward-tabs .tabs .tab {
        height: 38px;
        line-height: 38px;
    }

    .reward-tabs .tab a {
        color: #fff;
        background-color: #ccc;
    }

    .reward-tabs .tab a:hover {
        background-color: #ccc;
        color: #fff;
    }

    .reward-tabs .wechat-tab .active {
        color: #fff !important;
        background-color: #22AB38 !important;
    }

    .reward-tabs .alipay-tab .active {
        color: #fff !important;
        background-color: #019FE8 !important;
    }

    .reward-tabs .reward-img {
        width: 210px;
        height: 210px;
    }
</style>

<div id="reward">
    <a href="#rewardModal" class="reward-link modal-trigger btn-floating btn-medium waves-effect waves-light red">赏</a>

    <!-- Modal Structure -->
    <div id="rewardModal" class="modal">
        <div class="modal-content">
            <a class="close modal-close"><i class="fas fa-times"></i></a>
            <h4 class="reward-title">你的赏识是我前进的动力</h4>
            <div class="reward-content">
                <div class="reward-tabs">
                    <ul class="tabs row">
                        <li class="tab col s6 alipay-tab waves-effect waves-light"><a href="#alipay">支付宝</a></li>
                        <li class="tab col s6 wechat-tab waves-effect waves-light"><a href="#wechat">微 信</a></li>
                    </ul>
                    <div id="alipay">
                        <img src="/medias/reward/alipay.jpg" class="reward-img" alt="支付宝打赏二维码">
                    </div>
                    <div id="wechat">
                        <img src="/medias/reward/wechat.png" class="reward-img" alt="微信打赏二维码">
                    </div>
                </div>
            </div>
        </div>
    </div>
</div>

<script>
    $(function () {
        $('.tabs').tabs();
    });
</script>

            
        </div>
    </div>

    

    

    

    

    

    

    

    

    

<article id="prenext-posts" class="prev-next articles">
    <div class="row article-row">
        
        <div class="article col s12 m6" data-aos="fade-up">
            <div class="article-badge left-badge text-color">
                <i class="fas fa-chevron-left"></i>&nbsp;上一篇</div>
            <div class="card">
                <a href="/2022/02/19/SpringBoot/7-Web%E5%BC%80%E5%8F%91-%E5%AE%9E%E6%88%98%E6%A1%88%E4%BE%8B/">
                    <div class="card-image">
                        
                        
                        <img src="/medias/featureimages/18.jpg" class="responsive-img" alt="Spring Boot 开发实战">
                        
                        <span class="card-title">Spring Boot 开发实战</span>
                    </div>
                </a>
                <div class="card-content article-content">
                    <div class="summary block-with-text">
                        
                            
                        
                    </div>
                    <div class="publish-info">
                        <span class="publish-date">
                            <i class="far fa-clock fa-fw icon-date"></i>2022-02-19
                        </span>
                        <span class="publish-author">
                            
                            <i class="fas fa-bookmark fa-fw icon-category"></i>
                            
                            <a href="/categories/Spring-Boot/" class="post-category">
                                    Spring Boot
                                </a>
                            
                            
                        </span>
                    </div>
                </div>
                
                <div class="card-action article-tags">
                    
                    <a href="/tags/Spring-Boot-%E5%BC%80%E5%8F%91%E5%AE%9E%E6%88%98/">
                        <span class="chip bg-color">Spring Boot 开发实战</span>
                    </a>
                    
                </div>
                
            </div>
        </div>
        
        
        <div class="article col s12 m6" data-aos="fade-up">
            <div class="article-badge right-badge text-color">
                下一篇&nbsp;<i class="fas fa-chevron-right"></i>
            </div>
            <div class="card">
                <a href="/2022/02/17/RPC/RPC%20%E5%85%AB%E8%82%A1%E6%96%87/">
                    <div class="card-image">
                        
                        
                        <img src="/medias/featureimages/17.jpg" class="responsive-img" alt="RPC 常见面试题">
                        
                        <span class="card-title">RPC 常见面试题</span>
                    </div>
                </a>
                <div class="card-content article-content">
                    <div class="summary block-with-text">
                        
                            
                        
                    </div>
                    <div class="publish-info">
                            <span class="publish-date">
                                <i class="far fa-clock fa-fw icon-date"></i>2022-02-17
                            </span>
                        <span class="publish-author">
                            
                            <i class="fas fa-bookmark fa-fw icon-category"></i>
                            
                            <a href="/categories/RPC/" class="post-category">
                                    RPC
                                </a>
                            
                            
                        </span>
                    </div>
                </div>
                
                <div class="card-action article-tags">
                    
                    <a href="/tags/RPC/">
                        <span class="chip bg-color">RPC</span>
                    </a>
                    
                </div>
                
            </div>
        </div>
        
    </div>
</article>

</div>



<!-- 代码块功能依赖 -->
<script type="text/javascript" src="/libs/codeBlock/codeBlockFuction.js"></script>

<!-- 代码语言 -->

<script type="text/javascript" src="/libs/codeBlock/codeLang.js"></script>


<!-- 代码块复制 -->

<script type="text/javascript" src="/libs/codeBlock/codeCopy.js"></script>


<!-- 代码块收缩 -->

<script type="text/javascript" src="/libs/codeBlock/codeShrink.js"></script>


    </div>
    <div id="toc-aside" class="expanded col l3 hide-on-med-and-down">
        <div class="toc-widget card" style="background-color: white;">
            <div class="toc-title"><i class="far fa-list-alt"></i>&nbsp;&nbsp;目录</div>
            <div id="toc-content"></div>
        </div>
    </div>
</div>

<!-- TOC 悬浮按钮. -->

<div id="floating-toc-btn" class="hide-on-med-and-down">
    <a class="btn-floating btn-large bg-color">
        <i class="fas fa-list-ul"></i>
    </a>
</div>


<script src="/libs/tocbot/tocbot.min.js"></script>
<script>
    $(function () {
        tocbot.init({
            tocSelector: '#toc-content',
            contentSelector: '#articleContent',
            headingsOffset: -($(window).height() * 0.4 - 45),
            collapseDepth: Number('0'),
            headingSelector: 'h1, h2, h3, h4'
        });

        // modify the toc link href to support Chinese.
        let i = 0;
        let tocHeading = 'toc-heading-';
        $('#toc-content a').each(function () {
            $(this).attr('href', '#' + tocHeading + (++i));
        });

        // modify the heading title id to support Chinese.
        i = 0;
        $('#articleContent').children('h1, h2, h3, h4').each(function () {
            $(this).attr('id', tocHeading + (++i));
        });

        // Set scroll toc fixed.
        let tocHeight = parseInt($(window).height() * 0.4 - 64);
        let $tocWidget = $('.toc-widget');
        $(window).scroll(function () {
            let scroll = $(window).scrollTop();
            /* add post toc fixed. */
            if (scroll > tocHeight) {
                $tocWidget.addClass('toc-fixed');
            } else {
                $tocWidget.removeClass('toc-fixed');
            }
        });

        
        /* 修复文章卡片 div 的宽度. */
        let fixPostCardWidth = function (srcId, targetId) {
            let srcDiv = $('#' + srcId);
            if (srcDiv.length === 0) {
                return;
            }

            let w = srcDiv.width();
            if (w >= 450) {
                w = w + 21;
            } else if (w >= 350 && w < 450) {
                w = w + 18;
            } else if (w >= 300 && w < 350) {
                w = w + 16;
            } else {
                w = w + 14;
            }
            $('#' + targetId).width(w);
        };

        // 切换TOC目录展开收缩的相关操作.
        const expandedClass = 'expanded';
        let $tocAside = $('#toc-aside');
        let $mainContent = $('#main-content');
        $('#floating-toc-btn .btn-floating').click(function () {
            if ($tocAside.hasClass(expandedClass)) {
                $tocAside.removeClass(expandedClass).hide();
                $mainContent.removeClass('l9');
            } else {
                $tocAside.addClass(expandedClass).show();
                $mainContent.addClass('l9');
            }
            fixPostCardWidth('artDetail', 'prenext-posts');
        });
        
    });
</script>

    

</main>




    <footer class="page-footer bg-color">
    
        <link rel="stylesheet" href="/libs/aplayer/APlayer.min.css">
<style>
    .aplayer .aplayer-lrc p {
        
        display: none;
        
        font-size: 12px;
        font-weight: 700;
        line-height: 16px !important;
    }

    .aplayer .aplayer-lrc p.aplayer-lrc-current {
        
        display: none;
        
        font-size: 15px;
        color: #42b983;
    }

    
    .aplayer.aplayer-fixed.aplayer-narrow .aplayer-body {
        left: -66px !important;
    }

    .aplayer.aplayer-fixed.aplayer-narrow .aplayer-body:hover {
        left: 0px !important;
    }

    
</style>
<div class="">
    
    <div class="row">
        <meting-js class="col l8 offset-l2 m10 offset-m1 s12"
                   server="netease"
                   type="playlist"
                   id="503838841"
                   fixed='true'
                   autoplay='false'
                   theme='#42b983'
                   loop='all'
                   order='random'
                   preload='auto'
                   volume='0.7'
                   list-folded='true'
        >
        </meting-js>
    </div>
</div>

<script src="/libs/aplayer/APlayer.min.js"></script>
<script src="https://cdn.jsdelivr.net/npm/meting@2/dist/Meting.min.js"></script>

    

    <div class="container row center-align"
         style="margin-bottom: 15px !important;">
        <div class="col s12 m8 l8 copy-right">
            Copyright&nbsp;&copy;
            
                <span id="year">2019-2022</span>
            
            <span id="year">2019</span>
            <a href="/about" target="_blank">Gtwff</a>
            |&nbsp;Powered by&nbsp;<a href="https://hexo.io/" target="_blank">Hexo</a>
            |&nbsp;Theme&nbsp;<a href="https://github.com/blinkfox/hexo-theme-matery" target="_blank">Matery</a>
            <br>
            
                &nbsp;<i class="fas fa-chart-area"></i>&nbsp;站点总字数:&nbsp;<span
                        class="white-color">577.4k</span>
            
            
            
                
            
            
                <span id="busuanzi_container_site_pv">
                &nbsp;|&nbsp;<i class="far fa-eye"></i>&nbsp;总访问量:&nbsp;
                    <span id="busuanzi_value_site_pv" class="white-color"></span>
            </span>
            
            
                <span id="busuanzi_container_site_uv">
                &nbsp;|&nbsp;<i class="fas fa-users"></i>&nbsp;总访问人数:&nbsp;
                    <span id="busuanzi_value_site_uv" class="white-color"></span>
            </span>
            
            <br>

            <!-- 运行天数提醒. -->
            
                <span id="sitetime"> Loading ...</span>
                <script>
                    var calcSiteTime = function () {
                        var seconds = 1000;
                        var minutes = seconds * 60;
                        var hours = minutes * 60;
                        var days = hours * 24;
                        var years = days * 365;
                        var today = new Date();
                        var startYear = "2019";
                        var startMonth = "6";
                        var startDate = "28";
                        var startHour = "0";
                        var startMinute = "0";
                        var startSecond = "0";
                        var todayYear = today.getFullYear();
                        var todayMonth = today.getMonth() + 1;
                        var todayDate = today.getDate();
                        var todayHour = today.getHours();
                        var todayMinute = today.getMinutes();
                        var todaySecond = today.getSeconds();
                        var t1 = Date.UTC(startYear, startMonth, startDate, startHour, startMinute, startSecond);
                        var t2 = Date.UTC(todayYear, todayMonth, todayDate, todayHour, todayMinute, todaySecond);
                        var diff = t2 - t1;
                        var diffYears = Math.floor(diff / years);
                        var diffDays = Math.floor((diff / days) - diffYears * 365);

                        // 区分是否有年份.
                        var language = 'zh-CN';
                        if (startYear === String(todayYear)) {
                            document.getElementById("year").innerHTML = todayYear;
                            var daysTip = 'This site has been running for ' + diffDays + ' days';
                            if (language === 'zh-CN') {
                                daysTip = '本站已运行 ' + diffDays + ' 天';
                            } else if (language === 'zh-HK') {
                                daysTip = '本站已運行 ' + diffDays + ' 天';
                            }
                            document.getElementById("sitetime").innerHTML = daysTip;
                        } else {
                            document.getElementById("year").innerHTML = startYear + " - " + todayYear;
                            var yearsAndDaysTip = 'This site has been running for ' + diffYears + ' years and '
                                + diffDays + ' days';
                            if (language === 'zh-CN') {
                                yearsAndDaysTip = '本站已运行 ' + diffYears + ' 年 ' + diffDays + ' 天';
                            } else if (language === 'zh-HK') {
                                yearsAndDaysTip = '本站已運行 ' + diffYears + ' 年 ' + diffDays + ' 天';
                            }
                            document.getElementById("sitetime").innerHTML = yearsAndDaysTip;
                        }
                    }

                    calcSiteTime();
                </script>
            
            <br>
            
        </div>
        <div class="col s12 m4 l4 social-link social-statis">
    <a href="https://github.com/kuangtianyu" class="tooltipped" target="_blank" data-tooltip="访问我的GitHub" data-position="top" data-delay="50">
        <i class="fab fa-github"></i>
    </a>



    <a href="mailto:1575235124@qq.com" class="tooltipped" target="_blank" data-tooltip="邮件联系我" data-position="top" data-delay="50">
        <i class="fas fa-envelope-open"></i>
    </a>







    <a href="tencent://AddContact/?fromId=50&fromSubId=1&subcmd=all&uin=1575235124" class="tooltipped" target="_blank" data-tooltip="QQ联系我: 1575235124" data-position="top" data-delay="50">
        <i class="fab fa-qq"></i>
    </a>





    <a href="https://www.zhihu.com/people/kuang-tian-yu-59" class="tooltipped" target="_blank" data-tooltip="关注我的知乎: https://www.zhihu.com/people/kuang-tian-yu-59" data-position="top" data-delay="50">
        <i class="fab fa-zhihu1">知</i>
    </a>



    <a href="/atom.xml" class="tooltipped" target="_blank" data-tooltip="RSS 订阅" data-position="top" data-delay="50">
        <i class="fas fa-rss"></i>
    </a>

</div>
    </div>
</footer>

<div class="progress-bar"></div>


    <!-- 搜索遮罩框 -->
<div id="searchModal" class="modal">
    <div class="modal-content">
        <div class="search-header">
            <span class="title"><i class="fas fa-search"></i>&nbsp;&nbsp;搜索</span>
            <input type="search" id="searchInput" name="s" placeholder="请输入搜索的关键字"
                   class="search-input">
        </div>
        <div id="searchResult"></div>
    </div>
</div>

<script type="text/javascript">
$(function () {
    var searchFunc = function (path, search_id, content_id) {
        'use strict';
        $.ajax({
            url: path,
            dataType: "xml",
            success: function (xmlResponse) {
                // get the contents from search data
                var datas = $("entry", xmlResponse).map(function () {
                    return {
                        title: $("title", this).text(),
                        content: $("content", this).text(),
                        url: $("url", this).text()
                    };
                }).get();
                var $input = document.getElementById(search_id);
                var $resultContent = document.getElementById(content_id);
                $input.addEventListener('input', function () {
                    var str = '<ul class=\"search-result-list\">';
                    var keywords = this.value.trim().toLowerCase().split(/[\s\-]+/);
                    $resultContent.innerHTML = "";
                    if (this.value.trim().length <= 0) {
                        return;
                    }
                    // perform local searching
                    datas.forEach(function (data) {
                        var isMatch = true;
                        var data_title = data.title.trim().toLowerCase();
                        var data_content = data.content.trim().replace(/<[^>]+>/g, "").toLowerCase();
                        var data_url = data.url;
                        data_url = data_url.indexOf('/') === 0 ? data.url : '/' + data_url;
                        var index_title = -1;
                        var index_content = -1;
                        var first_occur = -1;
                        // only match artiles with not empty titles and contents
                        if (data_title !== '' && data_content !== '') {
                            keywords.forEach(function (keyword, i) {
                                index_title = data_title.indexOf(keyword);
                                index_content = data_content.indexOf(keyword);
                                if (index_title < 0 && index_content < 0) {
                                    isMatch = false;
                                } else {
                                    if (index_content < 0) {
                                        index_content = 0;
                                    }
                                    if (i === 0) {
                                        first_occur = index_content;
                                    }
                                }
                            });
                        }
                        // show search results
                        if (isMatch) {
                            str += "<li><a href='" + data_url + "' class='search-result-title'>" + data_title + "</a>";
                            var content = data.content.trim().replace(/<[^>]+>/g, "");
                            if (first_occur >= 0) {
                                // cut out 100 characters
                                var start = first_occur - 20;
                                var end = first_occur + 80;
                                if (start < 0) {
                                    start = 0;
                                }
                                if (start === 0) {
                                    end = 100;
                                }
                                if (end > content.length) {
                                    end = content.length;
                                }
                                var match_content = content.substr(start, end);
                                // highlight all keywords
                                keywords.forEach(function (keyword) {
                                    var regS = new RegExp(keyword, "gi");
                                    match_content = match_content.replace(regS, "<em class=\"search-keyword\">" + keyword + "</em>");
                                });

                                str += "<p class=\"search-result\">" + match_content + "...</p>"
                            }
                            str += "</li>";
                        }
                    });
                    str += "</ul>";
                    $resultContent.innerHTML = str;
                });
            }
        });
    };

    searchFunc('/search.xml', 'searchInput', 'searchResult');
});
</script>

    <!-- 回到顶部按钮 -->
<div id="backTop" class="top-scroll">
    <a class="btn-floating btn-large waves-effect waves-light" href="#!">
        <i class="fas fa-arrow-up"></i>
    </a>
</div>


    <script src="/libs/materialize/materialize.min.js"></script>
    <script src="/libs/masonry/masonry.pkgd.min.js"></script>
    <script src="/libs/aos/aos.js"></script>
    <script src="/libs/scrollprogress/scrollProgress.min.js"></script>
    <script src="/libs/lightGallery/js/lightgallery-all.min.js"></script>
    <script src="/js/matery.js"></script>

    <!-- Baidu Analytics -->

    <!-- Baidu Push -->

<script>
    (function () {
        var bp = document.createElement('script');
        var curProtocol = window.location.protocol.split(':')[0];
        if (curProtocol === 'https') {
            bp.src = 'https://zz.bdstatic.com/linksubmit/push.js';
        } else {
            bp.src = 'http://push.zhanzhang.baidu.com/push.js';
        }
        var s = document.getElementsByTagName("script")[0];
        s.parentNode.insertBefore(bp, s);
    })();
</script>

    
    <script src="/libs/others/clicklove.js" async="async"></script>
    
    
    <script async src="/libs/others/busuanzi.pure.mini.js"></script>
    

    

    

    <!--腾讯兔小巢-->
    
    
    <script type="text/javascript" color="0,0,255"
        pointColor="0,0,255" opacity='0.7'
        zIndex="-1" count="99"
        src="/libs/background/canvas-nest.js"></script>
    

    
    
    <script type="text/javascript" size="150" alpha='0.6'
        zIndex="-1" src="/libs/background/ribbon-refresh.min.js" async="async"></script>
    

    
    <script type="text/javascript" src="/libs/background/ribbon-dynamic.js" async="async"></script>
    

    
    <script src="/libs/instantpage/instantpage.js" type="module"></script>
    

</body>

</html>
